New shiftable magnetic shift registers, more commonly known as racetrack memory, may be a solution for our growing need for faster and cheaper high capacity memory. Racetrack memory could become a viable alternative to current forms of data storage. For instance, mechanical disk drives provide high capacity storage at a low cost, but mechanical drives are fundamentally unreliable due to their many moving parts. Solid state drives provide relatively reliable storage, but at a high cost for low capacity. Racetrack memory should allow high capacity storage at a fraction of the cost of solid state memory. However, additional improvements would make racetrack memory a more cost-effective and reliable alternative.
The general design of racetrack memory has been documented. See, e.g., U.S. Pat. No. 6,834,005, issued Dec. 21, 2004, entitled, “Shiftable Magnetic Shift Register and Method of Using the Same,” the disclosure of which is incorporated herein by reference. The basic mechanism for racetrack memory involves the use of a fine track made of magnetic material. The track may be magnetized in small sections, or domains, in one direction (e.g., representing a bit value of “0”) or in the opposite direction (e.g., representing a bit value of “1”). An electric current is applied to the track to rapidly move or shift the domains along the track. As the domains move along the track, a reading device or “head,” situated at a fixed location beside the track, can read the domains “bit-by-bit.” In the alternative, a writing device or “head,” situated at a fixed location beside the track, can change the bit value of a given domain by magnetically altering the direction of the magnetic moment stored within the given domain.
The direction and speed of movement of the domains along the magnetic track is controlled by both the magnitude and direction of the electric current. Further, the amount of time during which the electric current is applied also affects the movement of the domains along the track. Ideally, one controlled pulse of electric current should move the domains one domain distance or increment along the track. However, one issue with conventional racetrack memory designs is maintaining consistent domain movements. Even if the applied electric current is consistent, the domains may shift at different rates and/or distances at each electric pulse or shift cycle. Further, even if no current is applied, the domains may move in the rest state, modifying the stored data and resulting in erroneous data reads.
In order to address inconsistent and/or spontaneous domain movements, experts have proposed “pinning” the locations of the domains. This technique involves physically notching the magnetic track at fixed intervals to clearly define the borders of the domains. To a limited extent, pinning does yield more consistent domain movements; however, pinning does not fully address spontaneous drifting of the domains along the magnetic track.